Would the added real estate of a 75 permit them to live well? I'd really like to keep them but I'm not going to force them into a smaller tank just because I want to keep them.
Plans on going 125+ in the future, if I can't keep them in a 75, I know what I'll put in the bigger tank in the future!
Also, if he is fine to live as a single male, would he be fine in a 4' tank?